I think you're talking about the infamous "double-specialty". If a Wizard is a Universalist, he may specialize in one of his Order's schools upon becoming a Wizard of High Sorcery. If he is *already* specialized in one of his Order's schools, he may then take a third (or a second, if you're a white robe Diviner) forbidden school to get an additional bonus.
The schools that you can "double-specialize" in are clearly stated in the text of the PrC. If you are a Diviner that becomes a Red Robe, for example, you cannot get super-charged Divination spells. That's not one of your Order's schools.
It should police itself in the text, but the short answer is no. If you are an Abjurer that becomes a White Robe, and you choose to focus on Abjuration, you get the bonus. If you are an Abjurer that takes the Red Robes, your Abjuration spells cannot be boosted.
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